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Quoted from here So why code for an obsolete version. If your host uses only RedHat and Redhat is going to keep you in the past I would say find another host. If Redhat can not mke there system work with PHP 5.2 that is there problem not oscommerce's problem. If you have a script that doesn't work with php 5.2 see if the maker has an update for it. Not upgrading by choice is one thing but being told you can't is another.
The PHP 5.3 is said to make 5.2 obsolete also.

They probably thought that if you were adding the shipping module that you were using a production ready version, not one that the core wasn't finished on. I may be wrong but they may not think of it as an add-on since it comes with the basic install.

Get more choices with this one
http://addons.oscommerce.com/category?search=UPS+Shipping
This looks like it may do what you want.
http://addons.oscommerce.com/info/818
here is a real old version.
http://addons.oscommerce.com/info/511

I would use this one if your running an rc version.
http://addons.oscommerce.com/info/5743
If not use version 3.31 of the one your looking at. Then if you have any problems see if there was a fix posted for it. I did not have some of the problems that fixs were posted for.